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Re: [Qemu-devel] OVMF Google Summer of Code ideas

From: Gleb Natapov
Subject: Re: [Qemu-devel] OVMF Google Summer of Code ideas
Date: Wed, 9 Mar 2011 12:16:27 +0200

On Tue, Mar 08, 2011 at 09:13:38AM -0800, Jordan Justen wrote:
> 2011/3/8 Gleb Natapov <address@hidden>:
> > On Tue, Mar 08, 2011 at 07:18:09AM +0000, Stefan Hajnoczi wrote:
> >> > Regarding the non-volatile variables issue, I have been trying to
> >> > develop a proposal for addressing this with a change to QEMU's
> >> > hardware support of bios.bin.  But, I don't have the suggestion (or
> >> > implementation) ready at this time.
> >>
> >> Sounds like something to keep discussing with the QEMU and SeaBIOS
> >> communities.  Gleb Natapov and Kevin O'Connor have done a lot of the
> >> recent BIOS and firmware interface work.  I think persistent CMOS has
> >> come up several times and might be similar to non-volatile UEFI
> >> storage.
> >>
> > What kind of information OVMF stores on a persistent storage?
> Non-volatile variables are a general system wide environment variable
> storage facility, but one key thing to store (for instance) is the
> path to the boot image.
> > CMOS
> > memory is less them 512 byte IIRC and this may not be enough. What OVMF
> > uses on real HW for non-volatile storage?
> Regarding CMOS, I think qemu exposes 128 bytes of non persistent CMOS
> RAM.  Many current chipsets provide another bank of 128 bytes, meaning
> a total of 256 bytes (minus the RTC registers).
> Regarding UEFI non-volatile variables on real HW:
> Most systems today have at least 1MB of flash storage located just
> below 4GB.  The entire contents can be modified, which is how firmware
> updates happen.
How this flash storage is programmed? May be we can emulate something

> For a UEFI based system, the non-volatile variables generally occupy
> 8KB~64KB of the flash depending on flash space availability.
> -Jordan


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